1. Field of the Invention
The present invention relates to subsea hydrocarbon production. More particularly, the present invention the relates to systems and methods for remediating solid hydrates that may accumulate in a subsea location associated with the hyrdrocarbon production. Additionally, the present invention relates to systems whereby heated water can be delivered from a subsea location to an area of the accumulated hydrates.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
There is often a need for heat to be delivered to a subsea location. In particular, in the offshore oil and gas industry, it is important to be able to supply heat to a desired location. Under certain circumstances, oil and gas wells are in locations in which presssure and temperature conditions cause the gases to form a solid hydrate. The hydrates are basically methane- or hyrdrocarbon-type ice. Hydrates are likely to form under conditions of high pressures and low temperatures. Although hydrates may form at any water depth, hydrate formation occurs most commonly in deep water. For example, at about one-thousand feet and below, the water temperature remains relatively constant, just slightly above freezing in the vast majority of the world's oceans. The pressure, however, dramatically increases with depth. This affects hydrate formation. In general, the deeper the water, the more critical the problem hydrates become for oil company operations. Typically, hydrate formation becomes an issue at approximately 1500 feet. Below 3000 feet, such hydrate formations present serious problems for the oil and gas companies.
The solid hydrate can form a blockage within a pipeline and can severely reduce or completely block the product flow of oil and/or gas. Hydrate formations also occur at other locations, for example, externally on a subsea wellhead. Hydrates have also been formed externally on the connector on the subsea wellhead and the lower marine riser package. This can result in frozen latches that prevent the connector from releasing.
In the past, companies have attempted to address the hydrate issue by installing hydrate traps in their pipelines. The hydrate trap is basically a loop inside of a pipeline that is specific to hydrate remediation. The installed hydrates trap is intended to generate the heat to remediate the hydrates plugs or ice. However, hydrate formation is problem for existing subsea pipelines having no hydrate traps as well as for subsea wellheads and associated equipment mounted thereon.
In the past, attempts have been made in an effort to apply heat to the hydrate formation. When heat is applied in an uncontrolled manner, there is a possibility that the heated hydrates could expand to the extent that a pressurized pipe could burst. Additionally, those prior attempts have been unable to store heat while the heat source is being re-energized. As such, a need has developed to be able to modulate the heat source so as to adapt to the particular hydrate formation. Additionally, there is a need to be able to store heat while the heat source is being energized.
Typically, when working in the subsea environment at significant depths, remotely-operated vehicles (ROVs) are used. ROVs are typically hydraulic-operated. In the past, attempts have been made at subsea hydrate remediation with the use of electric heaters powered by an ROV system. Unfortunately, typical ROV systems do not have sufficient electrical power to generate the heat necessary to effectively remediate such formations.
As such, it is desirable to provide a system and method for performing subsea hydrate remediation by using heat. It is also desirable to have a system and method for performing such hydrate remediation by using heat produced in a subsea location. It is further desirable to have a system and method for performing subsea hydrate remediation that can be delivered to a desired location by an ROV.
In the past, various patents have issued relating to such hydrate remediation activities. For example, U.S. Pat. No. 7,234,523, issued on Jun. 27, 2007 to B. J. Reid, describes a hydraulic friction fluid heater. This method includes pumping a fluid through a length of tubing such that the temperature of the fluid increases. The temperature increase of the fluid is created by friction in the tubing. It can also be created by at least one pressure reducing device, such as an orifice, a pressure reducing valve, or relief valve. A subsea structure may be heated by transferring heat from fluid circulating in a closed loop configuration or by direct application of fluid to the subsea structure by using a nozzle. A remotely operated vehicle may be utilized to transport some or all of the equipment necessary and to provide power to the pumps used for circulating fluid through the tubing.
U.S. Pat. No. 6,939,082, issued on Sep. 6, 2005 to B. F. Baugh, provides a subea pipeline blockage remediation method. This method involves the use of a remotely-operated vehicle on the ocean floor to land on and move along a subsea pipeline located above the seafloor. Electrically heated seawater is repeatedly circulated across the outer surface of the pipeline to melt hydrates which have formed on the inside of the pipeline.
U.S. Pat. No. 6,415,868, issued on Jul. 9, 2002 to Janoff et al., teaches a method and apparatus for preventing the formation of alkane hydrates in subsea equipment. This apparatus has at least one flow path through which a well fluid is permitted to flow. The well fluid has a flow temperature and a lower hydrate formation temperature at which hydrates will form in the well fluid. A temperature control device is provided which comprises a housing positioned in heat exchange relationship with respect to the flow path and a phase change material disposed in the housing. The phase change material has a melting point which is below the flow temperature but above the hydrate formation temperature. When the temperature of the phase change material drops to its melting point, the phase change material will solidify and its latent heat will be transferred to the well fluid to maintain the temperature of the well fluid in the flow path above its hydrate formation temperature.
U.S. Pat. No. 5,803,161, issued on Sep. 8, 1998 to Wahle et al., provides a heat pipe heat exchanger for cooling or heating high temperature/high-pressure sub-sea well streams. This heat exchanger has an annular reservoir surrounding a section of pipeline adjacent the wellhead. One or more heat pipes extend from the annular reservoir into the seawater. In a heat removal configuration, a working fluid is contained within the annular reservoir. The working fluid boils and is evaporated by heat from the wellstream fluid and forms a vapor which rises upwardly into and is condensed within the heat pipes so as to release heat into the surrounding seawater. The recondensed working fluid flows back down into the reservoir to repeat the cycle. In a heat-providing configuration, the working fluid is contained in the heat pipes so as to be boiled by heat transferred from the surrounding seawater. The resulting vapor rises upwardly into the annular reservoir and the heat is transferred to the cooler wellstream fluids.
U.S. Pat. No. 6,776,227, issued on Aug. 17, 2004 to Beida et al., discloses a wellhead heating apparatus and method which serves to prevent freeze-off of wellhead equipment. Radiant heat from a flameless heater is utilized to heat fluid in a heat exchanger, such as a tank or finned radiator. A pump is used to circulate the heated fluid through a conduit loop deployed in thermal contact with the equipment to be heated, such that the heat from the fluid is transferred to the equipment. The equipment is maintained it at sufficient temperature to prevent freeze-off.
U.S. Pat. No. 6,260,615, issued on Jul. 17, 2001 to Dalrymple et al., shows a method and apparatus for de-icing oilwells. A power cable is used for heating well bores in cold climates. An electrical switch is located within a wellbore at a selected location in the power cable. The electrical switch is provided to selectively short out the conductors within the power cable so as to allow the power cable above the switch to be used as a resistive heating element to thaw the wellbore.
U.S. Pat. No. 7,036,596, issued on May 2, 2006 B. J. Reid, provides a hydraulic friction fluid heater and method. The method includes pumping a fluid through a length of tubing such that the temperature of the fluid increases. The temperature increase of the fluid is created by friction in the tubing. A subsea structure may be heated by transferring heat from fluid circulating in a closed loop configuration or by direct application of fluid to the subsea structure using a nozzle. A remotely operated vehicle may be utilized to transport the equipment necessary.
U.S. Pat. No. 7,669,659, issued on Mar. 2, 2010 to M. R. Lugo, teaches a system for preventing hydrate formation in chemical injection piping for subsea hydrocarbon production. This system has a manifold, a production piping communicating with the manifold, a chemical injection line positioned in heat exchange relationship along the production piping, and a fluid delivery system connected to the chemical injection line for passing a heated fluid through at least a portion of the chemical injection line. The chemical injection line has a first portion affixed to a surface of the production piping and a second portion extending outwardly therefrom. The fluid delivery system is in communication with the second portion of the chemical injection line. The chemical injection line extends in a U-shaped pattern or in a spiral pattern around an outer surface of the production piping.
It is an object of the present invention to provide a system and method for preventing hydrate formation in subsea locations.
It is another object of the present invention to provide a system and method for preventing hydrate formations in which the heated water is delivered from a subsea location.
It is another object of the present invention to provide a system and method for preventing hydrate formations whereby the heated water can be delivered to a desired location through the use of a ROV.
It is another object of the present invention to provide a system and a method for preventing hydrate formations that can be modulated to the particular hydrate formation.
It is a further object of the present invention to provide a system and a method for preventing hydrate formations that can store heat while the system is being energized.
It is still a further object of the present invention to provide a system and method for preventing hydrate formations which is easy to use, relatively inexpensive, and easy to manufacture.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.